Tube and pole piece assembly



June 5, 1962 M. J. LAvx-:RTY ETAI. 3,037,800

TUBE AND POLE PIECE ASSEMBLY 2 Sheets-Sheet 1 Filed Feb. 5, 1957 INVENToRs /l//AT/NJ LAVEETY CARL BKUNNER A 7h. am

Leads `lune 5, 1962 M. J. LAVERTY ETAL TUBE AND POLE PIECE ASSEMBLY Filed Feb. 5, 1957 2 Sheets-Sheet 2 I,prI,...II',laplpllfllllp'r'la'An Figi 6 INVENT071S5 @1mg-1355 Y ATTORNEY iinited States 'Ihis invention relates to a tube-pole piece assembly such as used in circuit breakers, and more particularly to methods and 'apparatus for attaching the pole piece to the tube and the structure produced thereby. p

The tube-pole piece assembly as utilized in a circuit breaker comprises generally a hydraulically sealed nonmagnetic tube closed at one end by a pole piece; i.e., a magnetic member. Contained within the tube are a movable pole piece and a spring for retarding the movement of the movable pole piece towards the stationary pole piece. The tube is also preferably filled with 'a liquid to dampen further the movements of the pole piece. The tube is surrounded by a coil of wire which conducts the circuit current so that `the electromagnetic field generated by the ow of current passes through both pole pieces. The stiifness of the spring and the viscosity of the liquid is chosen so that during normal current flow, there is little or practically no tendency for the movable pole piece to travel towards the end p'ole piece. An armature is located in close proximity to the end pole piece and is so coupled to the circuit breaker contacts that if the armature is 'attracted and moved to the pole piece, the contactsare opened and the circuit is interrupted. Under conditions of normal current iiow, the pole pieces are physically separated and the magnetic flux through the end pole piece is insufficient to attract the armature. If a short circuit occurs, the current surge through the coil produces an electromagnetic field of such magnitude that the flux through the end pole piece is sufficient to attract the armature and open the circuit. The two circuit conditions thus far described, namelynormal and short circuit, are the extreme conditions, the intermediate condition is the overloaded circuit. In the usual overloaded condition there is insufficient flux passing through the end pole piece to attract the armature; however, there is an electromagnetic eld of sufficient intensity traversing the movable I pole piece causing it to move gradually towards the stationary pole piece. When the movable one contacts the stationary pole piece, the reluctance of the magnetic circuit is considerably reduced thereby increasing the intensity of the magnetic ux through the pole pieces to such an extent that the armature is `attracted to the end pole piece to open the circuit. It should be `apparent that the tubepole piece assembly acts as a time-delay device, permitting a continuous overload condition to exist for a predetermined time before interrupting the circuit. Thus, in the industry, the tube-pole piece assembly is known as a hydraulic-magnetic time delay tube.

This invention relates to the tube and end pole piece assembly and particularly to the method and apparatus for attaching the pole piece to the end of the tube and the novel structure produced thereby.

In accordance with conventional practice, the tubes are made by drawing from suitable sheet metal, e.g., brass. This method of manufacture is similar to that used in making cartridge cases and produces a thin walled tube of required accuracy and uniformity which is integrally closed at one end. It has vbeen 'the practice to part'the closed end and replace it with a pole piece of magnetic material. The pole piece is brazed or silver soldered to the end of the tube in order to hydraulically seal the tube. This technique necessitates the use of flux and high temperatures Which cause oxidation and leaves undesirable ux residuals which are removed by washing, pickling, rinsing and drying. The reasons for cleaning the tube arent O 3,037,800 Patented June 5, 1962 are to remove `all particles which might impede movement of the movable parts within the tube and to eliminate the possibility of chemical reaction between the hydraulic liquid and the metal parts. Thus, the conventional practice suffers from the following disadvantages: The silver solder is expensive, the brazing andv subsequent cleaningoperations are slow and expensive, the tubes `are occasionally leaky, caused by faulty joints, and the method is not amenable -to mass production techniques.

Accordingly, it is an object of -this invention to provide a method for attaching the end pole piece to the tube so as to overcome each of the above-mentioned disadvantages.

It is a first feature of this invention to use the drawn tube without cutting-off the integrally closed end.

It is a further feature of our invention to attach the pole piece to the tube by mechanical interlocking means and thereby obviate the necessity vfor solder, flux, heat and subsequent cleaning operations.

A still further feature of lthis invention is to provide a tube and pole piece assembly including an additional part of non-magnetic material for mounting and locating the assembly in the circuit breaker. The yadditional part is attached to the pole piece at the same time that the pole piece is attached to the tube so that the pole piece, tube and mounting member are mechanically interlocked to form a single unitary structure.

It is a further object of this invention to provide novel apparatus for mechanically interlocking the pole piece to the tube.

It is a still further object of this invention to provide a novel tube and pole piece assembly.

In accordance with a fust broad aspect of our invention, there is provided a method for attaching a pole piece to ya tube, comprising positioning the pole piece on the tube, and deforming an inner edge of the pole piece in an inwardly radial direction, causing the edge to bite into the surface of the tube.

In accordance with a second aspect of our invention, there is provided a punch for aixing the pole piece to the tube comprising a block, and a swaging tool having two concentric portions separated sufficiently to permit the `wall of the tube to fit into the cylindrical space. On the end of the outer cylindrical portion, a cylindrical projection is provided close to the space between the cylindrical portions. The pole piece and tube are supported so that when the punch is operated, the block acts against one s urface of the pole piece and the swaging tool acts against the opposite surface thereof, with sufficient force to impress the surface with the projection, thereby displacing the inner edge of the pole piece in an inwardl radial direction to bite into the tube.

In accordance with a third aspect of the invention, there is provided a tube and pole piece assembly characvterized by an inside edge of the pole piece being of smaller diameter than the outside diameter of the tube, and a slug wedged in the tube adjacent the pole piece and shaped to bite into the tube along a circumference adjacent the other inside edge of the pole piece.

The above-mentioned and other features and objects of this invention and `the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional View of the tube and pole piece assembly mounted on a block;

FIG. 2 shows the swaging tool in relation to the block and tube-pole piece assembly;

FIG. 3 is a cross-sectional view of the finished assembly;

FIG. 4 is an enlarged View of the seal between the tube and pole piece; y

FIG. 5 shows another embodiment of the invention;

FIG. 6 is a cross-sectional View of the iinished assembly produced by the embodiment of FIG. 5; and

' FIG. 7 is an enlarged view of tlie seal between the tube i and the pole piece.v

` Although we have chosen to use the expression tube and pole piece, which properly delines the components as used in a circuit breaker, it isV to be realized thatV our inventionhas much wider application and, therefore, ex-

pressions which define the mechanical equivalents such asV tube and annular member, tube and iiange may be used interchangeably. Y.

Referring now to FIGS. 1-4, there is illustrated the preferred embodiment of our invention. f f In accordance with the first feature of this invention, we utilize the tube with the integrally closed end, shown at 1, 2 respectively which assuresv the hydraulic sealV required between the pole piece 3 and the tube 1. The pole annular portion 18 displaces the metal in opposite radial directions, thereby also wedging the washer 18 against the extension portion 17. It is to be realized that the peripheral shape of the washer may take any desired form, eg., circularor rectangular. It is only essential that the opening of the washerY conform to the shape of the pole piece 3 is an annular member iittingsnuglyon the tube 1 and the two components Vare `supported imposition by a `block 4, or'anvil, V,which in this'embodiment is station-V ary. A cup-shaped slug, or disk, 5,withthe cup portion facing the anvil 4, is inserted .intoV the tube 1.` The purpose oi' the' slug 5 and its shape will become clear from the following discussion.` Y vv AReferring now to FIG. 2, there is shown a swaging tool 6 comprising two concentricicylindrical portions 7, v8

spaced sutiicientlyapart to permit thewall of the tube to pass therebetween. AOn the end of the outer cylindricalV member 7 there is formed a concentric projection 9,hav

ydown* with sutcient force to effect a'rnechanical inter-V lock along two circumferential lines of the tube. First, the projection 9 deforms the pole piece 3 Yby impressing the V in the surface thereof, causing part of the metal of the pole piece to be displaced in aninwardly radial direction, and to bite into the tube as shown at'w12, FIGS. 3, 4. The length and'width o f the V are importantV and determined by empirical methods. h lf'the length is excessive, the pole piece may be sheared or weakened, and

both ythese seals to escape.

piece on which it is placed. Y

One advantage which flows from the second embodiment is that open ended tubes may be utilized, since the pole piece, as -swaged in'place, is mechanically sealed tothe tube at two circumferential lines 20 and 21, FIG. 7.` Therefore, any hydraulic leakage must pass through A second ladvantage is that the Washer 18 is secured in place during the swaging Y operation.

While we have described above the principles of our i invention in connection with Specific apparatus, it is to if the width of the V is not sufficient, the amount of metal f displaced will be inadequate to lock the pole piece to the tube. The size of the VV depends on the size of the pole piece and the materials from which the tube and pole piece are made. y h h h The second mechanical interlock ismade as a result of the inner cylinder 8, attening the Vslug and wedging it in place. Since the circumferential edge of the slug is cylindrical, the edge 13 of the slug 5 bites into the tube along a line adjacent theropposite inner edge 14 ofthe pole piece 3. The mechanical interlock is seen clearly in FIG. 4

which is an enlargement of portonfA of FlG. 3.

The tube is made of anon-magnetic material such as .brass and the slug and pole piece are made of a magnetic Y material such as steel.

' Referring now to FIGS. 5-f7, there is illustrated a secring the tube in the circuit breaker.

In this embodiment the slug 5 and tube 1 are mounted Yon the swaging tool 6 as shown. The Washer 18 is placed over the pole piece and the two parts are inverted for l' be clearly understood that this description is made only byrway of example and not as a limitation to the scope of our invention as set forth in the objects thereof andv in the accompanying claims.

What is claimed is:

1. An assembly of Va tube, an external ange and an internal slug, the tube being of softer material than either the flange or the slug and having uniform inside and outside diameters substantially along its entire length and irregular inside and outside diameters at one end thereof, saidrliange comprising an annular portion mounted on said tube contiguous to said end and having an inside edge of smaller diameter than the uniform outside diameter of said tube whereby said edge bites into said tube reducing the uniform outside diameter thereof locally, and Vsaid internal slug being located inside said tube adjacent said end and surrounded by said flange, said slug having an outside edge of greater diameter than the internal uniform diameter of the tube whereby said edge bites into the wall Yof the tube increasing the inside diameter of the tube locally.

2. The assembly according lto claim 1 wherein said tube is closed at one end and said annular portion and said slug respectively surround the wall contiguous to said closed end.

3. The assembly according to claim 2 wherein the maximum diameter of said internal slug is adjacent the closed end of said tube and the minimum inside diameter of the annular portion is offset from the plane of the maximum diameter of said slug, whereby a positive mechanical locking of the three parts in xed 'and perma nent relationship to each other is achieved.

References Cited in the file of this patent UNITED STATES PATENTS 521,825

Shipe June 26, 1894 801,683 Penfold Oct. l0, 1905 924,398 Stevens June 8, 1909 1,190,803V Rosenfeld July 1l, 1916 1,320,501 Shrum lNov. 4, 1919 1,614,606 Esterow Ian. 18, 1927 1,641,269 Hoke Sept. 6, 1927 1,704,228 Tibbetts Mar. 5, 1929 1,706,118 Hopkins Mar. 19, 1929 1,714,708 Winning May 28, 1929 1,752,982 Herold Apr. 1, 1930 1,939,553 I-lillret al Dec. 12, 1933 2,005,267 Rehder June 18, 1935 2,217,000 Eames Oct. 8, 1940 2,646,613 Enzler July 28, 1953 2,772,472 Ballon Dec. 4, 1956 2,840,113 Simpson et al June 24, 1958 

